The Simplex Process for the synergistic gasification of coals, especially caking coals, encapsulated in a matrix of cellulosic waste materials such as municipal solid waste (MSW) or biomass, is highly cost-effective in producing a clean synthesis or fuel gas. This novel process makes possible for the first time the use of a shaft furnace of blast furnace geometry and dimensions to achieve high productivities in a moving bed gasifier operated at slagging temperatures.
The Simplex Process simultaneously provides an environmentally benign solution to a pollution problem by turning, for example, MSW preferably with dewatered sewage sludge (DSS) admixed with coal into an energy resource, and it produces a clean-burning, medium-heating-value fuel gas at a cost that is competitive with imported petroleum. In a preferred embodiment, the Simplex Process makes possible the efficient utilization of the abundant energy-intensive Eastern bituminous caking coals which have hitherto defied processing in a simple, moving-bed gasifier because of their well-known tendency to swell, melt, coalesce, and polymerize when passing through the temperature range from 900.degree. to 1300.degree. F. The use of the caking coal is accomplished by carefully blending a mixture of shredded, air-classified organic solid waste with crushed caking coal (including fines associated therewith) and then compacting the mixture either prior to or in the process of feeding said mixture to the Simplex gasifier.
It has been found that a number of useful and unexpected advantages accrue when the feed or burden is prepared as more fully described herein. Thus, it is well known that the Lurgi process for the gasification of coal, which is the most firmly established coal gasification process in the world today, is subject to the following disadvantages:
(1) It cannot process caking coals because of the tendency of such coals to agglomerate, bridge, and polymerize when heated to a temperature where they become thermoplastic.
(2) It cannot process crushed coal containing fines but must be screened to eliminate such fines which then constitute a disposal problem.
(3) The upward gas velocity is limited by the small particle size of the coal processed, which in turn limits the permissible productivity per square foot of converter cross-section in the gasification zone.
(4) It has been limited in maximum, practicable furnace size to vessels of approximately 13 feet in diameter so that it requires 26 Lurgi converters to produce the synthesis gas for a single 250 million SCFD SNG plant.
The above limitations of the successful Lurgi gasifier have been experienced on an even larger scale by the blast furnace, which is the heart of the steel industry and one of the sustaining pillars of the Industrial Revolution. The successful operation of the blast furnace, which incidentally functions as a large gasifier, is critically dependent on careful preparation of its three-component burden or feed mixture, i.e., iron ore, coke, and limestone. These components must be carefully sized and blended to insure smooth operation of the gravitating bed without disruptive channelling of the large volume of hot ascending gases produced in the furnace. Careful burden preparation has made it possible to operate these gas producing blast furnaces when scaled to the prodigious diameter of 42 feet. The resulting economies of large scale operation have a decisive impact on the capital and production costs.
The art of pressing coal into briquettes has been known for a century. There, the objective has been principally to utilize coal fines by compacting them into a more easily handled and stored fuel. Similarly, the compaction of household refuse or municipal solid waste is well known. Householders may purchase commercial devices that will form trash and refuse into larger pellets that are more efficiently stored and transported and that occupy less volume in a sanitary landfill. The compaction or pelleting of municipal refuse together with waste coal products has also been proposed. Thus, Jackman in U.S. Pat. No. 3,910,775 discloses the briquetting of coal including coal fines with organic wastes. Jackman makes no mention of the ratios of coal and organic waste and makes no specific reference to problems attendant upon the use of caking coal and in fact, he does not differentiate between the use of different types of coal. He is primarily concerned with the ability to use high sulfur waste coal and is particularly concerned with using fines, although he does mention employing crushed coal.
Apparently, in Jackman the use of minor quantities of acidic coal fines (derived from coal washings or "dirty sulfurrich unusable coal") is for the purpose of reducing the pH of the sewage stream being filtered through the prepared briquettes so as to precipitate phosphates present in the waste water. The ratios of the components, the physical characteristics of the novel shaped articles, the primary function of these articles, the choice of the coal component in certain embodiments of Applicant's contribution to the art are not disclosed in Jackman who in fact mentions none of these.
It has also been proposed in the art to employ organic solid waste with coal which also can contain oil, in Kaiser U.S. Pat. No. 3,841,851. No mention is made of briquetting. It is furthermore significant that Kaiser (who is contemporaneous with Jackman) in his working example in columns 8-9 utilized only 10% coal, 10% residual fuel oil, and 80% dried household refuse.